<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>练习</title>
    <style>
        .c1{
            width: 200px;
            height: 200px;
            border: 100px solid;
            border-color: red green blue purple;
            border-radius: 50%;
        }
    </style>
</head>
<body>
<div class="c1"></div>
</body>
</html>